1. Technical Field of the Invention
The present invention relates to an optical control element and an optical control element array which are preferably useful in, for example, an on-demand digital exposure device that is used in a photolithography step, an image forming device due to digital exposure, a projection display device such as a projector, and a microdisplay device such as a head mounted display, and also to a method of producing such an optical control element. The invention relates also to a wavefront control element and a wavefront control element array for ultraviolet, visible, and infrared lights, and electromagnetic waves of longer wavelengths.
2. Description of the Related Art
As a micro-electro mechanical optical control element in which the MEMS (Micro-Electro Mechanical Systems) technique is used, for example, a GLV element (Grating Light Valve) using a diffraction grating, a DMD element (Digital Mirror Device) using minute deflecting mirrors, an optical control element based on Fabry-Perot interference, and an optical control element using total internal reflection (TIR) are known. Such optical control elements are practically used.
The MEMS technique is an element technique for electrically displacing or moving a micro structure on the order of micrometers. A typical production method for the MEMS technique is a microprocessing technique which is used in a semiconductor process technology.
Among the above optical control elements, for example, a GLV element is disclosed in U.S. Pat. No. 5,459,610. As shown in FIG. 22, the disclosed GLV 1 has a structure where plural (five or six) beams 5 respectively formed by thin films in which both ends are supported are arranged on an Si substrate 3 in a stripe pattern. A metal reflective film 7 made of Al or the like is disposed on the upper face of each of the beams 5. Below the beams 5, a common lower electrode 11 is formed on the substrate 3 via a gap 9. Usually, the beams 5 have a width of about 3 μm, and a pitch of about 5 μm.
When a voltage is applied between the lower electrode 11 and one of the metal reflective films 7 on the upper faces of the beams, an electrostatic force acts therebetween, and the corresponding beam 5 is flexed toward the substrate 3 to be vertically displaced. In the initial state, the beams 5 are at the same level, and the metal. reflective films on the upper faces operates as a usual total reflection mirror, so that incident light is regularly reflected. When a voltage is applied to alternate ones of the beams 5 to cause the applied beams 5 to be displaced, and the level difference between the beams and the not-displaced beams 5 is λ/4 (λ is the wavelength of the light), the incident light is diffracted. Therefore, the incident light can be controlled to be regularly reflected or to be diffracted, depending on whether a voltage is applied or not applied.
In addition to the above-described optical control element, JP-A-11-119122, JP-A-2000-180737, JP-A-2000-180739, JP-A-2000-121966, and JP-A-2002-221678 relate to the present invention.
In all related optical control elements, one pixel (a minimum unit for controlling light) has only one displaceable structural member, or, as in a GLV element, several one-dimensional structural members (the beams 5 shown in FIG. 22).
In the field of optics, it is known that dot-like structural members which are two-dimensionally arranged exert various optical functions. When the shape and arrangement period of the dots are in the range from the order of λ (wavelength) to about 20λ, for example, light diffusion, light scattering, diffraction, interference, and the like occur. When they are shorter than the wavelength and in the level of λ/2, an optical phenomenon due to the photonic band effect occurs. When they are shorter than about λ/10, optical functions due to an index-controlled material based on the structural property, or the quantum optics effect are exerted. Namely, the structure of microdots or nanodots which are two-dimensionally arranged largely affects the optics. When the structure can be controlled by the MEMS technique, it is possible to realize various optical function elements.
In the related art, however, only several beams on the order of micrometers are displaced as in the GLV element described above, and there is no optical control element in which displacements of two-dimensionally arranged microdots or nanodots are controlled to exert an optical function.
Even if two-dimensionally arranged dots are individually controlled, a large number of drive portions for controlling displacements are required, and the area efficiency is poor. Therefore, this configuration cannot be practically used. Furthermore, when dots are independently formed and controlled, the shapes and properties of the dots are largely dispersed, and there arise the possibility that the quality and reliability of the dots are lowered.